1. Field of the Invention
The invention relates to novel vaccine compositions, including immunocontraceptive vaccines, and particularly to novel adjuvants for use therein.
2. Description of the Prior Art
Gonadotropin releasing hormone (“GnRH”, also known as Luteinizing Hormone Releasing Hormone, or “LHRH”), has long been recognized as being of central importance to the regulation of fertility in animals. GnRH is a decapeptide which has the same amino acid sequence, i.e., pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-GlyNH2 (SEQ ID NO. 1) in all mammals. Closely related GnRH compounds have also been identified in other non-mammals, including fowl, and receptors for GnRH have been identified in reptiles and amphibians. In males and females, GnRH is released from the hypothalamus into the bloodstream and travels via the blood to the pituitary, where it induces the release of the gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH). These two gonadotropins, in turn, act upon the gonads, inducing steroidogenesis and gametogenesis. In growing male animals, the gonadotropins stimulate the development of the testes and the synthesis of testicular steroids. In the growing female animal the development of the ovaries is stimulated and therein follicle development, synthesis of ovarian steroids and ovulation. Steroids released from the gonads into the circulation also act upon various other tissues.
In recent years, GnRH neutralization has been used as an effective means of contraception in a variety of animals. Fraser described that the gonadotropin hormonal cascade can be halted by neutralization of the biological activity of GnRH (Physiological Effects of Antibody to Luteinizing Hormone Releasing Hormone. In: Physiological Effects of Immunity Against Reproductive Hormones, Edwards and Johnson, Eds. Cambridge University Press, 1976). As a consequence of GnRH neutralization, the gonadotropins and gonadal steroids are not released into the blood, interrupting the hormonal regulation of fertility and ceasing gametogenesis. In addition to the use of immunization against GnRH for animal sterilization to prevent breeding, the immunization has also been suggested for the treatment of aggressiveness in male animals such as dogs and bulls, chemical castration of male animals for slaughter, prevention of heat in female animals, and prevention of restlessness in male animals being fattened for slaughter, and reduction of boar taint in the meat of pigs raised for slaughter.
Neutralization of GnRH has also been employed for the treatment of a number of other diseases. A number of important diseases, including breast cancer, uterine and other gynecological cancers, endometriosis, uterine fibroids, prostate cancer, and benign prostatic hypertrophy, are also affected by gonadotropins and gonadal steroid hormones. Neutralization of the patient's GnRH effectively eliminates the gonadal steroids that induce and stimulate these diseases. See McLachlan et al., 1986, British Journal of Obstetrics and Gynecology, 93:431-454; Conn and Crowley, 1991, New England Journal of Medicine, 324:93-103; Filicori and Flamigni, 1988, Drugs, 35:63-82.
GnRH neutralization has been typically achieved by the induction or introduction of anti-GnRH antibodies in the subject animal or patient. These antibodies may be induced by active immunization with GnRH immunogens, or by passive immunization by administering anti-GnRH antibodies (Fraser, 1976, ibid). Antibodies to GnRH produce infertility by binding to circulating endogenous GnRH, precluding the GnRH from binding to its pituitary receptor and thereby interfering with its ability to release FSH and LH. The severe reduction or absence of these hormones leads to atrophy of the gonads and concomitant infertility in both sexes as described above.
Despite these advantages, active immunization against GnRH has not been widely practiced due to deficiencies associated with the GnRH vaccines. The prior art anti-GnRH vaccines have typically lacked the potency necessary to effect long-term contraception in a single dose. In fact, immunocontraception has traditionally required at least two doses, a prime and a boost, for long-term efficacy. The prime dose prepares the immune system for repeat antigen exposure and provides only a short term response. The subsequent boost immunization can result in an immune response which can be maintained for a period of months to years. In addition to the GnRH immunogen, an adjuvant is a necessary component of any vaccine intended for long-lasting immunocontraception.
At present, Freund's complete adjuvant (FCA) is the only adjuvant that has provided high and long-lasting immunocontraceptive responses. Although many other adjuvants have been developed, none have been able to achieve the high antibody titers obtained using Freund's complete adjuvant. Freund's complete adjuvant includes a emulsion of killed bacteria of Mycobacterium tuberculosis or M. butyricum (also known as M. smegmatis) in mineral oil with a surfactant.
Despite the efficacy achieved with Freund's complete adjuvant, numerous concerns have been raised over its use in animals, and particularly in animals raised for human consumption. One primary concern has been the potential for false-positive TB skin tests in an animal which has been injected with FCA containing killed M. tuberculosis (Tizard, 1977, An Introduction to Veterinary Immunology, CRC Press, Boca Raton, Fla.). Other concerns over the use of FCA have included fears that it may be carcinogenic and that it may cause intense cell-mediated immune responses which produce lesions at the site of injection.